Smoke sensors, such as commercial smoke sensors, often located inside of a housing or enclosure, use near infrared light scattering inside a small plastic chamber located inside of the enclosure, with inlets of controlled dimensions to prevent entry of unwanted particles. However, some unwanted airborne particles do make their way into the chamber, causing false alarms. Over time, these particles may also collect at the inlets of the sensor chamber, making it more difficult for smoke particles to diffuse into the chamber.
A photoelectric sensor is operative on the basis of light scattering to detect particles as the particles travel through the chamber. From an efficiency perspective, detection is most efficient with particles that are at least the size of approximately one-half the wavelength of (visible) light—approximately 0.5 microns (or larger). Synthetic materials, which are increasingly being included in household items, may produce small particles that are less than 0.5 microns when burned. Such small particles may go undetected for a relatively long amount of time during a flaming fire. On the other hand, it may be difficult to distinguish the presence of large smoke particles (such as those particles that may be produced during a smoldering fire) from other objects or airborne particles. For example, it can be difficult to distinguish large particles resulting from a fire from steam or dust. Still further, it can be difficult to distinguish a fire from nuisance scenarios (e.g., cooking scenarios, such as operating a toaster, pouring alcohol into a boiling pot, etc.).
Eliminating the chamber would increase the exposure of a sensing element (e.g., photoelectric sensor) to smoke. Unfortunately, simply eliminating the chamber would also expose the sensing element of the sensor to high intensity ambient light, which would flood the sensing element and prevent the sensor from detecting smoke.